This invention relates to carbonate polymers and more particularly to those carbonate polymers that have powdered additives dispersed therein.
Carbonate polymers derived from reactions of dihydroxyorganic compounds, particularly the dihydric phenols, and carbonic acid derivatives such as phosgene have found extensive commercial application because of their excellent physical properties. These thermoplastic polymers are suitable for the manufacture of molded parts wherein impact strength, rigidity, toughness, heat resistance and excellent electrical properties are required.
The industry often uses concentrates of powdered additive and a carrier resin for introducing said additives to synthetic thermoplastic materials. In these concentrates, carrier resins are intimately blended with large amounts of additives. The carrier resin then acts in the concentrate as a kind of solution promoter between the "dilution" (i.e., thermoplastic) material and additive thereby providing a product with the additive homogeneously dispersed therein.
The making of carrier resin/additive concentrates, which are also called "master batches," is done in a manner similar to the preparation of other thermoplastic resins containing additives except that a particularly high ratio of additive is necessary and the blended material is eventually comminuted to a granulate. It is evident that the use of bonding agents is desirable for bonding such large amounts of additives to the carrier resin of the master batch.
Esterified polysaccharides may be used as bonding agents for mixing carrier resins and powdered additives. However, such a bonding agent causes undesirable yellowing of the resulting blend, and thus adversely affects the reliability of a good color match of thermoplastics prepared in different batches. Further, the esterified polysaccharides are generally difficult to handle at ambient temperatures due to their high viscosities. Heating such additives just prior to blending to lower the viscosity of such agents limits their practical use from the standpoint of handling.
It is therefore desirable to provide efficient, color-stable bonding agents for adhering colorants and other powdered additives to carbonate polymer particles during blending and handling just prior to compounding.